Nature 390, 591–594; (1997)

Hypercycles are based on second-order (or higher) autocatalysis and defined by two or more replicators that are connected by another superimposed autocatalytic cycle. Our study describes a mutualistic relationship between two replicators, each catalysing the formation of the other, that are linked by a superimposed catalytic cycle. Although the kinetic data suggest the intermediary of higher-order species in the autocatalytic processes, the present system should not be referred to as an example of a minimal hypercycle in the absence of direct experimental evidence for the autocatalytic cross-coupling between replicators.